Process of preparing metals with high-temperature fusing points such as tungsten andof preparing wire therefrom



Patented Nov. 29, 1927.

UNITED STATES PATENT OFFICE.

IRITZ KOREF, OF CHARLOTTENBURG, AND HANS ALTERTHUM, OF HALENSEE, NEAR BERLIN, GERMANY, ASSIGNORS TO GENERAL ELECTRIC COMPANY, A CORPORA- TION OF NEW YORK.

PROCESS OF PREPARING METALS WITH HIGH-TEMPERATURE FUSING POINTS SUCH AS TUNGSTEN AND OF PREPARING WIRE THEREFROM.

No Drawing. Application filed January 6, 1923, Serial No. 611,156, and in Germany August 17, 1922.

metals.

Heretofore the wire has been made from tungsten, for example, as follows: A bar of pressed tungsten powder is heated to a lllgl'l temperature until the powder is sintered into a body which consists of crystals more or less closely joined. This bar-like body is then subjected to the well-known hammering and drawing process at high temperatures and thereby transformed gradually from the brittle condition, which is the condition of the bar, to a ductile wire, that is,

one which is flexible and adapted to be drawn cold.

The sizes of the small grains of the crystalline bar cannot always be exactly controlled so that in practice the individual char es of metal give bars having grains of di erent sizes and even with the most uniform progress of mechanical working the wires are not exactly alike.

Among the objects of our invention are the following: to overcome the foregoing objection; to prepare tungsten bars in the form of a single crystal or in the form of only a few crystals; to prepare tungsten wire from bars of the above form, to provide other details of improvement in processes of the above character, tending to increase their efliciency and serviceability.

To accomplish the foregoing and other useful ends our invention consists of details hereinafter more fully set forth and claimed.

In the contemplated process, the tungsten bars are converted into a single crystal or into a few crystals. The properties of such a macro-crystal are always the same and are not subject to any chance variations. The macro-crystal is to be recognized from the fact that in case of weak etching it shows large uniformly reflecting surfaces and not surfaces which reflect differently from place to place; and further, in that it splits in accordance with natural cleavage planes and finally after strong etching it becomes angular in shape, even though round in the beginning.

The process may be carried out by sintering preliminarily and thereafter highly sintering again bars pressed from powdered metal after which they are kept for a considerable time in a vacuum or in an indifierent or reducing gas atmosphere at temperatures near the melting point of the metal. As a result the microscopic crystals of the powder become coarser, combining very gradually and almost uniformly until after a time which may be as much as several hours, a macroscopic crystal forms at one point which is much larger than all the others and which now absorbs its neighbors in a comparatively short timein a few minutes sometimes. The crystal may be thus increased to such an extent that finally the whole body may consist of a single crystal. Sometimes it occurs that several such crystals are formed at diflerent points, each of which then continues to grow independently until it comes in contact with its neighbor or neighbors of the same order of magnitude with which, however, it does not combine. The body then consists of several large crystals and it is possible, by mechanical sub-division, for example, to take several different pieces, each of which consists of a single macrocrystal. The time which elapses before crystallization occurs may be shortened by increasing the temperature.

With respect to the number of crystals formed during the process, it is found that they differ in the case of different batches of metal made in regular operation, but in metal taken from any one batch, it is sub stantially constant.

It is found desirable to carry on the process in a reducing atmosphere and that then the number of crystals produced may be influenced by a certain small moisture content in the atmosphere. To this end, the hydro gen used is preferably passed through sulphuric acid of a predetermined concentration. If the ingots of a given batch of tungsten metal are found to give about 8 to 10 crystals with well dried hydrogen from a given source, then if this same hydrogen is passed through 50% sulphuric acid, for example, the ingots from the same batch may be found to consist of only 3 to 5 crystals. If the moisture content is further increased, a single crystal results. However, too great not have t -the crystalline tungsten) softened condition, sub ected to the usual process of mechanical working, wherein after the reduction in diameter amounting to about 20%, it loses its elasticity mentioned above. This may be recognized by the fact that a iece cut out with parallel sides in case oft e slow rise of pressure, can no longer be compressed cold by even a small amount without splitting. In the further course of hammering andi'drawing, the ductility gradually develo s just as in the case of wire in the wellown process which is drawn from a bar in a small crystalline state. In this ductile condition, the metal is suitable for use in incandescent lamps.

The following rule may be followed in making single crystal tungsten: Crystallized ammonium paratungstate is transformed by heating to a red glow into tungstic acid. This is reduced in a porcelain tube furnace b means of hydrogen at about 1,000 deg. to tungsten metal powder. This power is resse into ingots and the ingots are eated for about half an hour at 1300 deg.

C. in order to give them the cohesion necessa for the further treatment. Then the b0 y reviously sintered in this manner is broug t to a temperature near the melting point or in'the neighborhood of 3000 C. in a very well dried stream of hydro en, by sending through it a low voltage a ternating current of high amperage. After'coolg, it can be determined by etching whether the desired crystallization has begun. This process of heating and checking up b etchmg is repeated until the body is trans ormed into one or more macro-crystals. If it consists of only one crystal, the remaining inots of this batch are heated for the same ength of time with hydrogen of the same degree of dryness. If, on the contrary, it consists of 10 macro-crystals, for example, the hydrogen in the next ingot is passed through a washin bottle with sulphuric acid and is eated in the same man ner. If then, a body consisting of a single crystal is obtained, the work is continued in the same manner, otherwise, the concentration of the sulphuric acid will be varied until this result is reached.

What we claim as new, and desire to secure by Letters Patent of the United States, I

1. The method of making tungsten wire which consists in first making a large brittle tungsten crystal and then working this crystal into a flexible and'ductile state.

2. The method of making tungsten wire which consists in compressing powdered tungsten, sintering it into a large brittle crystal and thereafter working the crystal into a flexible and ductile state.

3. The method of making tungsten wire which consists in compressing powdered tungsten, sintering it into a large crystal in an atmosphere of reducing gas, and thereafter working the crystal into a flexible and ductile state.

4. The method of making tungsten wire which consists in compressing" powdered tungsten, sinterin it into a large crystal in an atmosphere 0 reducing gas one of the constituents of which is oxygen and thereafter working the crystal into a flexible and ductile state.

5. The method of making tungsten wire which consists in compressing powdered tungsten, sintering it into a large crystal in an atmosphere of reducing gas which gas is provided beforehand with a proper proportion of oxygen compound and thereafter working the crystal into a flexible and ductile state.

6. The method of making tungsten wire which consists in compressing powdered tungsten, sintering it into a large crystal in an atmosphere of reducing gas which gas is provided beforehand with a. proper proportion of water and thereafter working the crystal into a flexible and ductile state.

7. The method of making tun sten wire which consists in first making a arge brittle tungsten crystal and then working the crystal while still hot into a flexible and ductile state. i

8. The method of making tungsten wire which consists in compressing powdered tungsten, sintering it into a large crystal in an atmosphere of reducing gas, and thereafter wor in the crystal while still hot into a flexible an ductile state.

9. The method of making tungsten wire which is ductile cold, characterized by the feature that at first a large tungsten single crystal is made, and this is worked through a brittle stage by mechanical workin until it passes over into a state in which it is flexible and ductile when cold.

In witness whereof, we have hereunto set our hands this 9th day of December, 1922.

FRITZ KOREE. HANS ALTERTHUM. 

